1. Field of the Invention
This invention generally relates to a ball pushing unit. More specifically, the present invention relates to an internally geared hub ball pushing unit configured to be mounted on a hub axle and comprising a circular arc-shaped fitting part configured to be fitted onto a hub axle, an operating body insertion recess that has the shape of a circular arc and is configured such that a gear change operating body serving to facilitate gear change operations can be inserted therein and turned there-within, and a ball pushing surface configured and arranged to contact a ball of a bearing.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle drive train.
Internally geared hubs for bicycles generally have a driver on which a sprocket is mounted and a hub shell arranged and configured to receive power from the driver. Such internally geared hubs employ bearings to rotatably support the hub shell on the driver and the hub axle. Each bearing basically comprises a ball pushing unit serving as an inner race that has a cone shaped ball pushing surface on an external circumferential surface thereof and is configured to screw onto the hub axle, a ball bearing unit serving as an outer race that has a cone-shaped ball bearing surface on an inner circumferential portion thereof and is provided on the driver or hub axle, and spherical bodies (balls) arranged between the ball pushing unit and the ball bearing unit in such a fashion as to contact both. Some internally geared hubs have a sleeve-like gear change operating body for executing gear change operations mounted rotatably on the external circumferential surface of the hub axle (for example, see Japanese Patent No. 3184230). The gear change operating body is arranged to rotate integrally with a cable anchoring body that is arranged such that the ball pushing unit is disposed between the cable anchoring body and the gear change operating body. The gear change operating body is configured to control the on-off status of a plurality of clutches at each rotational phase and thus must be arranged at a prescribed position in the circumferential direction. Consequently, the ball pushing unit is not mounted on the hub axle with a screw connection and, instead, is mounted in such a fashion that it cannot rotate but can move axially with respect to the hub axle. In order to configure the ball pushing unit such that the gear change operating body can be passed there-through toward the cable anchoring body and turned there-within, the internal circumferential surface of the ball pushing unit has a pair of circular arc-shaped operating body insertion recesses and a pair of circular arc-shaped fitting parts that is arranged between the pair of operating body insertion recesses and configured to fit onto the external circumferential surface of the hub axle. In a ball pushing unit having operating body insertion recesses formed in the internal circumferential surface thereof, the wall thickness of the ball pushing unit is smaller at the portion where the operating body insertion recesses are formed than at the portion where the fitting parts are formed. Consequently, the wall thickness varies along the circumferential direction more than in the case of a ball pushing unit that screws onto the hub axle. The pressure with which the ball pushing unit presses against the balls of the bearing is adjusted by tightening and loosening a nut member arranged on the axially outward facing side of the cable anchoring body.
With the conventional ball pushing unit provided with operating body insertion recesses described above, warping (deformation) of the ball pushing unit sometimes occurs when the nut member is tightened in order to adjust the pressure with which the ball pushing unit presses against the balls of the bearing. Since the wall thickness of the ball pushing unit varies along the circumferential direction when viewed in a side cross sectional view lying in plane perpendicular to the hub axle, when the ball pushing unit warps, the ball pushing surface deviates from its original circular shape such that the ball pushing surface becomes oval in the cross sectional view. As a result, there is the possibility that the durability (service life) of the bearing will decline.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved internally geared hub ball pushing unit. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.